1. Field of the Invention
This invention relates to a novel biocontrol formulation for the prevention of contamination of plants by toxins produced by fungi, i.e., toxigenic Aspergillus spp. and the control of seedling and root diseases. The novel biocontrol formulation comprises biocontrol agents and bioplastic carrier granules, Mater-Bi® granules. The biocontrol agents of the formulation can comprise non-toxigenic strains of Aspergillus spp. which are capable of inhibiting growth of fungi that produce aflatoxin and further capable of suppressing production of aflatoxin by the toxigenic fungi or the biocontrol agents can comprise Trichoderma virens strains capable of inhibiting damping off in horticultural plants. The present invention relates to a biocontrol strategy whereby the biocontrol formulation comprising a non-toxigenic A. flavus strain and Mater-Bi® is applied to crops as a method for reducing aflatoxin contamination in corn and other crop plants.
2. Description of the Relevant Art
Augmentative biological control is generally perceived as a pest management tactic that utilizes the deliberate introduction of living natural enemies to lower the population level of invasive pests (DeBach and Rosen. 1991. In: Biological Control by Natural Enemies, Cambridge University Press, Cambridge). Biological control has been utilized for more than 100 years in efforts to control a wide number of agricultural pests including fungi, insects, and weeds (Siddiqui and Mahmood. 1996. Biores. Technol. 58: 229-239; Stiling and Cornelissen. 2005. Biol. Control 34: 236-246). Biocontrol strategies have been implemented to control aflatoxin contamination in several important agricultural crops, such as peanut, cotton, and corn (Abbas et al. 2006. Biocontrol Sci. Technol. 16: 437-449; Cotty, P. J. 1994. Phytopathology 84: 1270-1277; Dorner et al. 1992. J. Food Protect. 55: 888-892). Aflatoxins are highly carcinogenic secondary metabolites produced by several species of Aspergillus section flavi, including A. flavus Link, A. parasiticus Speare, and A. nominus Kutzman, Horn and Hesseltime. Of these, A. flavus is the most abundant aflatoxin-producing species associated with corn (Abbas et al. 2004a. Can. J. Bot. 82: 1768-1775; Abbas et al. 2004b. Can. J. Microbiol. 50: 193-199; Abbas et al. 2008. J. Agric. Food Chem. 56: 7578-7585; Wicklow et al. 1998. Mycol. Res. 102: 263-268). A. flavus is readily isolated from diverse environmental samples; however, soil and crop residues are considered the natural habitat of this fungus (Abbas et al. 2008, supra). In addition, soil serves as a reservoir of conidia (spores) which can infect susceptible crops (Scheidegger and Payne. 2003. Toxin Rev. 22:423-459).
Management of aflatoxin-producing fungi in corn is a difficult task, requiring an integrated approach including optimization of agronomical practices (i.e. irrigation, fertilization, etc.). These practices promote the general health of corn and can reduce, but not eliminate aflatoxin contamination (Cleveland et al. 2003. Pest Manag. Sci. 59: 629-642). Consequently, there is a need for additional, practical and cost-effective strategies to limit aflatoxin contamination of corn (Cleveland et al., supra). One attractive option to supplement, but not supplant these agronomical practices is biological control. Aflatoxin biological control programs can truly be defined as bio-competition since they do not utilize parasites or diseases of the pest, but instead use atoxigenic Aspergillus spp. to competitively exclude toxigenic fungi. Further, other fungal biocontrol agents such as Trichoderma have the potential to inhibit and displace damping-off fungi and other soil born diseases on a wide range of horticultural crops (Paulitz and Belanger. 2001. Ann. Rev. Phytopathology 39:103-133; Elliott et al. 2009. Biocontrol Sci. Tech. 10:1007-1021).
Surveys conducted in multiple geographical regions have found that not all strains of A. flavus produce aflatoxins (Abbas et al. 2004a, supra; Cotty and Bhatnagar. 1994. Appl. Environ. Microbiol. 60: 2248-2251). Current biocontrol strategies rely upon the ability of non-aflatoxigenic strains to competitively exclude indigenous aflatoxin-producing Aspergilli (Cleveland et al., supra). Successful reduction of aflatoxin contamination through the introduction of competitive non-aflatoxin producing strains of A. flavus has been demonstrated in a number of crops, including corn (Dorner et al. 1992, supra; Dorner, J. W. 2005. In: Aflatoxin and Food Safety, Abbas, H. K., Ed., CRC Press, Taylor & Francis Group, Boca Raton, pp. 333-352). Biocontrol fungi are typically applied to soil as alginate pellets, pregelatinized starch-flour granules, or colonized grains (Dorner, J. W. 2008. Food Addit. Contam. 25: 203-208; Honeycutt and Benson. 2001. Plant Dis. 85: 1241-1248; Lewis et al. 1998. Plant Dis. 82: 501-506). Among some of the successful formulations, a pasta-like product (Pesta) and a coated hulled-barley formulation (Afla-Guard®) have proven to be effective for delivering non-aflatoxigenic strains of A. flavus, as well as other biocontrol fungi (Connick et al. 1998. Biol. Control 13: 79-84; Singh et al. 2007. Biores. Technol. 98: 470-473; Dorner, supra). Application of these protocols has also been shown to be highly effective in recent studies conducted by the USDA-ARS at the Stoneville, Miss. research station. In these efforts, Abbas et al. (2006, supra) demonstrated that aflatoxin contamination in corn is dramatically reduced by field application of non-aflatoxin producing A. flavus strain NRRL 30797 (K49). In Abbas et al. (2006, supra) conidia of the competitive non-aflatoxigenic strain were applied to soil as inoculated wheat grains.
Various biocontrol methods and formulations for effective control of toxigenic fungi in cotton, peanuts, and corn are known in the art, as discussed above. However, there still remains a need for formulations of biocontrol agents which are effective for ensuring the integrity and effectiveness of the biocontrol agent after long term storage, for facilitating handling, and for field application of the biocontrol agent. Novel granular bioplastic biocontrol compositions comprising non-aflatoxigenic and non-toxigenic A. flavus strains and methods of using a novel granular bioplastic biocontrol composition to effectively reduce aflatoxin contamination in corn and other crop plants are provided. The need for suitable formulation systems to deliver other fungi used in biological control of plant diseases is also evident. Thus, an example of the use of bioplastic material to deliver Trichoderma virens to control damping-off disease caused by Rhizoctonia solani is also disclosed.